Telephone trunking system.



A. H. DYSON.

TELEPHONE TRUNKING SYSTEM.

APPLIUATION FILED JAN. 22, 1907.

Patented Ja11.10,1911.

T SHEETS-SHEET 1.

A. H. DYSON.

TELEPHONE TRUNKING SYSTEM.

APPLIQAI'IOH IILED J'A1L22, 1907.

Patented Jan. 10,1911.

A. H. DYSON.

TELEPHONE TBUNKING SYSTEM.

APPLICATION FILED JAN. 22, 1901.

981,399. 0 Patented Jan. 10,1911.

H. DYSION. TELEPHONE TBUNKING SYSTEM.

APBLIOATIOH 21mm JAN. 22, 1907.

Patented Jan 10,1911.

1 SHEETS-SHEET 4.

Patented Jan. 10, 1911 A. H. DYSON." TELEPHONE TRUNKING SYSTEM.

APPLIOATION TILED IAILZZ, 1907.

Patented Jan.10,1911.

'7 SHEETS-BHEET 6.

1m: sssssssssssssssssssssssssssss c.

A. H. DYSON.

TELEPHONE TRUN KING 'SYS'IEM.

APPLIUATION FILED 31111.22, 1907.

981,399. Patented Jan. 10,1911.

BHBETS -SHEET 7. i

m W W mgU f -q fi 3 9/46 @gji UNITED STATES PATENT OFFICE.

ALFRED H. DYSON, or CHICAGO, L InoIs, assisnon, BY MESNE ASSIGNMENTS, 'ro KELLOGG SWITCHBOARD & SUPPLY COMPANY, a conronarron or ILLINOIS.

TELEPHONE TRUNKING SYSTEM.

To all whom it may concern:".

Be it known that I, ALFRED H. DYSON, a citizen of the United States, resident of Chicago, county of Cook, and State of Illinois, have invented new and useful Improvements in Telephone Trunking Systems, of which the following is a specification. l

As is well known, it is the usual practice in large cities where a very great number of subscribers are to be served, to divide-the territoryinto sections, terminating the lines of the subscribers of each section in switchboards located conveniently to the end of: having the subscribers lines as'short as may be. 3 In addition to the above indicated ad- 1 vantage-of saving in the length of the sub scribers lines,'su ch an arrangement is necessary where manually operated switchboards are em loyed because the best practice requires t at multiple switchboards be employed, and such switchboards have a limited capacity on account of the fact that each 0 erator must have within-her reach multip e springjacksfor each subscribers line. i

In a system such as that mentioned, the various exchanges are connected by trunk lines proportioned in number to the amount of trafilc passing bet-ween the various exchan es. I

It as been found where a number of changes are located in a single city that a very large proportion of the calls are for lines terminating in local exchanges otherthat the one in which the call originatedf and in somecities the percentage of calls re-' quired to be trunked from one exchange to another amounts to as much as eighty or ninety per cent. of the total calls. In such systems, the operator who first. handles the originating call at the local exchange is called an A operator, and the operator at the distant exchange who completes a connection to .the called line is usually calleda B operator; 'It has been the practice for an A operator receiving a call from a subscribers line at the local exchange to 'complete the connection to a subscribers line in the same exchange if such a subscribers line was called for; or, if a subscriberin iin other exchange was wanted, to communicate by order wire with a B operator in the distant exchange, the B operator handlin'g'only trunking calls. It has been found difficult Specification of Letters Patent.

efiiciently liandle.'- alum-e; :zzs

.for an operator acting an as A operatorlto Patented Jan. 10, 1911.

Application filed January 22, 1907. Serial-No. 353,517.

It is to such a system as that above described that my inventi on relates, its object bein .in :a general=wayito reduce as far as possi Ie, the work required of a n- A operator, and, by. means 10f ;electrically1 controlled switchin mechanism-to automatically distribute t e calls passing through the system among the A operatorsa'nd B operators, giving to each operator as 'much work as she can The present manner -in which calls be tween A operators and B operators are ordinarily handled is as follows: The A operator on receiving a signal from a calling subscriber inserts an answering lug of-a air into a jack of the calling su scribers ine, ascertainsthe exchange and number of the subscriber wanted, communicates with the B operator of the exchange wanted, by order wire, telling such operator the number of the subscriber wanted. The B operator then adi'ises the A operator of the designating number of the trunk which is to be used in terminating before the A operator in multiple springjacks and before the B operator in a plug, whereon theA operator will insert "is quite" expensive on- 4 account- 5 of'the opera tors time used incompleting each-connection.'- It has been found by car'efulis'tucly that it costs about twice as mucltjfor'bperatorsl hire, to put through a trunking call as it would cost were all lines terminated-in a 'completing the connection, the said trunk single exchange and each call was completed by a single. operator. The present trunking method not only causes two opcrators to take part in the connection, but as the number is repeated by the A operator to the B operator, the A operator in communicating with the B operator must as it were, get into step with other calls coming to the B operator from other A operators. This not only increases the item for operators hire but renders the completion of the connection over the trunk slow, so that a relatively large number of trunks are necessary, and it is impossible to get the highest efliciency out of those provided.

In accordance with my invention, the A operator does not converse with the B operator at all, neither is she required to use any cord and plugs in putting through a connection, but the apparatus with which she is rovided consists only of a number of signal amps which may be located upon a desk together with a number of distributing devices which may assume the form of keys for eachllamp signal equaling in number the number .of exchanges to which connections must be made. The said signal lamps are not individual to any particular subscribers line, but are preferably common to a plurality of lines, and selective switchin mechani'sm is lprovided for interchangcahly associating t e signals with the lines over which 'calls 'are being originated. Thus, when a calling subscriber removes his receiver at the substation, he sets in train of motion automatically controlled selective switching mechanism which connects his line to an operators signal associated with a set of keys before mentioned (which maybe called distributing keys) not in use; the operator observing the signal will connect her telehone set with the called subscribers line, earn the exchange wanted and throw over the key belonging to that exchange associated with the call lamp. A number of trunk lines are provided extending to each exchange, and the throwing over of a key by an operator will cause electrically controlled selective switching mechanism to be started'to connect an indifferent idle trunk line leading to the wanted exchange to conductors connected with the particular key operated, the selective switch selecting the trunk line leading to the distant exchange automatically picking outa trunk of an idle B operator, who then ascertains from the callin subscriber the number of the line wanted and completes a connection in the usual manner by a cord circuit forming the terminal of the trunk. In connection with."

-without making a preliminary test, the call signal being extended to the called subscriber, or a busy signal extended to the calling subscriber automatically, according to the idle or busy condition of the called line. The supervision of a connection put up in this manner rests wholly with the B operator. The ordinary double supervision being provided, when the connected subscribers replace their receivers, the two signals will be displayed, and the B operator in withdrawing the plug from the springjack of the called line, will cause the trunk switches to be automatically disconnected from her cord and from the key at the A operators position, restoring said key to normal, and

the same act will also cause the switching mechanism by which a calling subscribers line is connected to the signal circuitat the A operators position to be restored to normal. It is thus seen that the A operator has no work to do except that of learning the exchange wanted after noticing the display of a call signal and operating a key corresponding to the exchan e wanted associated with the call signal displayed. F urther steps in' the operation for completing a connection, and for. restoring the apparatus therein employed to normal, being effected by the B operator, whose" work is lightened to this extent that she does not have to designate a trunk or test called subscribers line.

As indicated, a telephone system organized in accordance with my invention may comprise a number of difierent exchanges -in each of which a part of the telephone -of a one-hundredline group may appear multipled at the banks of a number of selective switches provided in number proportio'ned to the number of co-existing calls expected from the group, theselective switches being arranged to automatically select and connect with the calling line on the removal of the receivers at .the substations. Associated witheach such selective switch and individual thereto, is asecond electrically controlled switch before whose movable contact members appear multiple contacts forming terminals of link-circuitse xtending to onev or "more A operat ors". sitions, .each link-circuit being there provi ed with a call signal and a plurality of keys, one for each exchange included in the system as a whole. Thus, each group of subscribers lines has associated with it a number of pairs of switches, any pair of which 'is capable of ing to the A operators positions may appear in groups of one hundred at the switches with which they are associated, and may be inultipled 'say, one hundred times, in which case, if the usual ten per cent. trunking be employed, a group of one hundred A operators link-circuits would serve a great group of one thousand subscribers lines; in "other words, the terminals of the A operators link may be multipled to the switch pairs of ten one hundred line groups of subscribers lines. Each of the switches employed to select A operator links is preferably arranged so that when not in use, its movable contacts are at a particular zero or normal position, so that when a switch is operated by the initiation of a call at a substation, its wipers in their search for an idle A; o'perators link, may wipe over the terminal contacts of said links in consecutive numerical order The said links are preferably assigned to the A operators in numerical order, that is, assuming that the A 0perators are placed at positions numbered 1,

2-3 and 4, etc., the link or links whose confacts are first engaged by the wipers of a started selective switch may be assigned to the first A operator, the next contacts to the second A operator, and so on, in Order that the first calls originating from a great group of lines may come to the first operator 5 position, and as the business increases and a greater number of calls co-exist from the great group, they may come to the succeedmg operators. The division of the links, constituting any group, among the A operators may be arranged in any preferred manner; for instance, the first twenty or thirty links may be. assigned to the first o era-tor, the second twenty or thirty to the second operator, and so on, or, if a large exchange be supposed including the lines of several thousand subscribers, in which case, under the assumed ten per cent. trunking, a plurality of groups consisting each of one hundred A operators links will be provided (one such group for each thousand lines), the first A Operator may have assigned to her the first link-circuits of each one hundred line groups of circuits, the second op-- erator the second link-circuits, and so on, the object being to automatically condense the incoming business at one end of thej A o'perators board until all link-circuits atone A operators position are in use when additional calls coming in will be distributed to the second-position, and so on along the switchboard. Any preferred arrzuwement of these groups of link-circuits may e employed, and I do not desire to be limited to those herein more specifically referred to.

Each group of switch pairs before described may be provided with a masterswitch which is operatively associated with each and'every line of the one hundred line group of lines which the particular switch pairs controlled by it, serve, the function of the said master-switch being, when a call is-initiated at a substation to start into operation a switch pair,- one of which "selects the calling line and the other the first idle link-circuit leading to an A operator.

The outgoing ends-of the link-circuits of the A operators are provided with terminal contacts which are multipled at each of the keys pertaining to that link-circuit of which, as before indicated, one is provided for each of the exchanges in the system.

For extending connections from A operators positions to B operators positions, a number of switch pair's largely similar to those before mentioned may be provided, one switch of a pairbeing adapted to establish connection with the outgoing ends of the A operators link-circuits. For each such group of a pair being adapted to s'electa trunk or link-circuit extending to a B operators position' at the wanted exchange, there being at least as many such groups of switch pairs as there are exchanges in the system, and the number included in each group being determined by the amount of business expected to exist at each exchange, and the number of A opera tors link-circuits. For each such group of switch pairs maybe provided a masterswitch operatively associated with the A operators link-circuit keys for the exchange to which the switch pair group controlled by the master-switch belongs. The keys of the A operators link-circuits include contacts connected to circuits for controlling the masterswitch, and contacts connected to multiplecon-tacts-appearing inthe banks of one set of switches of a group of switch pairs. The

other set of switches of a group-of switch pairs have before their wipers, multiple con tacts or trunks extending to-the Bcperators positions, their arrangements being prefer-H- ably similar to. thatrhereinbefore described with respect to the links leading to the A operators positions, namely such that the businessof'B operators positionswi'll' be 'con'-' densed at'oneend of the switchboard, the switches employed to selecttrunks having a fixed normal or zero position as beforemem tioned. a I I Vhen theA operator having learnedfrom the calling' subscriber what xchange-' is -wanted, depresses the key appropriate to the exchange wanted belonging to the signal dis} iao played before her, this act automatically causes the master-switch of the group of switch pairs for the wanted exchange to start an idle switch pair into operation. The depressing of the key also alters the normal electrical condition of its multiple contacts appearing at the banks of the switches of the switch pairs adapted to select them and renders said contacts selectable by one switch of the started pair; the other switch of the pair then selects a link at the first idle B operators position and a signal is displayed, in response to which the B operator inquires the number of the subscriber wanted, and on learning the same from the subscriber, completes the connection. The key operated by the A operator, which, it will be noted, is her only act after learning the exchange wanted, remains in its shifted position until the B operator withdraws the plug from the jack of the called subscribers line in res onse to the disconnect signal. When she oes so, the said key at the A operators position is automatically restored to normal as well as the two switch pairs employed in completing the connection from the calling subscriber to the B operator. The A operator thus has absolutely nothing to do with taking down a connection, and in fact, will not know when the conversation terminates or when her link-circuit employed therefor is freed and rendered available for use by other calling subscribers, and it is of no interest or'advantage that she should do so, her only work, as before indicated, being to distribute incoming calls among the various exchanges, a principal object of the iiivention being to reduce the work of the A operators in so far as may be to a minimum.

Referring to the drawings, Figure 1 consisting of four sheets illustrates a preferred organization of circuits embodying iny' iiii'ention, the four sheets when placed in numerical order with sheet 1 at the left and sheet 4 atthe right constituting a complete diagram. Fig. 2 illustrates a preferred form of master-switch mechanism adapted for use in connection with the circuits indicated at M and M in Fig. 1. Fig. 3 shows a top view of a circular selective switch mechanism adapted for use in connection with the circuits at E E F and F in Fi 1. Fl L is a side view of said switch mechanism, Fig.

5 a sectional view thereof, Fig. Ga rear view of a portion of the switch mechanism. Fig. 7 is a diagrammatic illustration of the preferred arrangement of circuit contacts of; theswitch mechanism. Fig. 8 shows a preferred A operators key structure. Figs. 9 and 10 thereo thereof.

Referring now more specifically to Fig. 1

as shown at. C, a subscribers station includes the usual transmitter, receiver, condenser and call-bell with the hook-switch 1 adapted on the removal of the receiver to disconnect the condenser and bell operatively from the telephone line, and to connect the transmitter and receiver therewith. The said substation C is connected with the exchange by the two limbs L and L of the telephone line which is provided at the exchange with the usual multiple jack terminals comprising contacts l52-153, and also with the additional multiple terminals 2224:26 which are inultipled in banks appearing before wipers 23-2527 of a lurality of line selecting switches such as The line selecting switch E and the trunk selecting switch E form a pair connected by the link conductor La-La. In the organization of the system there would be provided a number of pairs of switches E and E for the one hundred line group of substation lines among which the line of C is included, the number of switch pairs being determined by the amount of business expected from the group. Every one hundred line group of subscribers would be provided with its a propriate group of switch pairs E and Ten such switch pairs for one hundred lines would ordinarily be sufficient.

A master-switch mechanism M is. pro vided, one for the group of one hundred lines with branch conductors leading to each line of the group which it serves to the end that each line may control said mechanism T he said master-switch mechanism when operated from a substation is effective to start into operation from a normal position of rest an indifierentidle switch pair E-E' serving the line group ofthe calling line. The

of the calling line, while the other switch E automatically selects multiple contacts 535557 of the first idle link-circuit appearin g before an A operator and being there switch selects multiple contacts 22-2 %:26.

provided with the call signal 74mm the multiple associated distributing keys Hind l) K. et-c. one for each exchan emcluded in the system.

Each distributing key, DK for example, isv

provided with link conductors terminating in multiple contacts 99101-103, appeari ig before thewipers'100+1()2 104 of a,"

plurality 'jof trunk selecting switches such as F, each such switch beiiig adapted automatically to select the multiple terminals of the -key DK after the same is operated, by

the A operator; the said multiple contacts 99 101103 are associated with terminals of other distributing keysDK' for'ithe same exchange -perta ining to the same and other A operators 'posit'ion s. Eachsnch distributiing key DK is also etfective-whenoperated indifferent idle pair of a plurality of switch pairs such as 1 -1 the switches of a pair being united by the conductors Lb-LZ) of which the switch F as before indicated, selects the operated key DK and the other switch F selects the terminals 12(3--128 130 of the first idle trunk circuit appearing before a B operator at the distant exchange.

The multiple key DK may have connections similar to the key DK but its multiple terminals are to be considered associated with a different group of switches F, F, the switches F, paired with the switches F which are arranged to select contact-s of keys DK' being adapted to select the first idle trunk circuits leading to an exchange of the system other than that in which the trunks selectable by the switches Ff associated with the first key DK terminate. It will be understood that the key DK in addition to its multiple terminals before referred to has access to a second master-- switch mechanism M controlling. the switch pairs for the exchange to which the key DK to'o'ther keys DK of the operator to whom the link-circuit shown at A is assigned'and to other keys DK' for the same distant exchange of other A operators.

The switch pairsE-E' and FF' may all be located in the originating exchange, while the trunks T-T, each comprising but two conductors, extend from the origi-. n'ating exchange to the distant exchanges except of course, such trunks T-T as lead to'B operators in the same exchange as the A operator.

- The apparatus at the exchange individual to a subscribers line such as C, in addition to the multiple terminals before mentioned, includes a line relay 2 controllable from the substation, which relay has by its armature contacts control of the masterswitch M and also of the electrical condition of the multiple contacts 222426 to render them selectable by the line selectors E. In addition to the line relay, the individual cut-off relay 6 is provided for the line having the function of altering the normal connection of the line limbs LL' when connection is made to terminals of the line to complete the talking circuit of the line to its multiple terminals. The master-switch mech anism MI comprises a common differential relay 1O controlling the starting relay 11 which by its armatures 12 and 13, connected to wipers 17-16 is effective to start siun 1 ltaneously any switch pair E-E, of which the said wipers may be engaging terminals 20 19. The wipers 16-17-18 of the mas.- ter-switch normally rest in engagement with terminals of an idle switch pair EE, and the wiper 18 has connections with the relay 14 of the master-switch, which relay is op-' contact banks, the respective operating magnets OM and OM are provided, controlled by their operating relays OR and OR. These relays are originally controlled in the operation of the system by the masterswitch mechanism but after their initial operation, they are controlled over circuits extending from the respective private wipers 23 and M in order that they by their control of the operating ma determine the selection of contacts engaged by the private wipers 23 and 54: when said contacts are in a particular selectable electrical condition; Each switch is provided with its oil-normal spring. ON or ON shifted on the first movement of the, switch to cause the operation of the respective ofinormal relays ONRand ONE, The arma-,

ture mechanisms of these relays constitute the means by which the started switches are caused, as it were, to re-act upon the masterswitch mechanism to restore the armature of common relay 10 to normal and to effect the movement of the wipers 1617-18 in search of contacts of an idle switch pair as soon as particular pair has been started. By employing the otf-normal relays before mentioned controlled by oil -normal switches having a singlecontact only, I am enabled to avoid the use of a large number of such off-normal switch springs efi'ect-ing by an electromagneticcombination a result which itwould otherwise be necessary to effect by a more complicated off-normal mechanism combination, and I consider. that by the use gnets OM and OM may respectively, which relays are then. looked v causing continuous operation of the respective switches 1n the'same dlrection as that in which they originally operated untilthey reach the zero or normal point when the off- -normal switch is shifted to normalagain,

switches ON and ON, the off-normal relays ONE and ONE? and their-release relays R11 and RR- ;-;The -arrangement of thelr parts is generally similar .to those of the switches E, E and such differences as exist will be more particularly pointed out in the following narrative of operation. It being assumed that the subscriber at the substation illustrated at C desires his line to be connected with that of the subscriber whose substation is illustrated at D and whose line terminates in an exchange of the system other than that in which the line C terminates, the subscriber C removes his receiver fromhook lever 1 which closes a path for current as follows: from battery to normal contact of armature 8 over limb L, hook lever l, limbL', back contact of armature 7, through relay 2 to ground. Said relay in attracting its armature 5 completes a locking circuit for itself from ground through the attracted armature 5, normal contact of armature '9, left-hand winding of relay 1.0, to battery. The attraction of armature t removes ground from the private contacts 22 of the line at the. line selectors E, while armature?) connects the active side of the battery with sleeve contacts 152 of the line spring-jacks, through a suitable protective resistance, thus rendering the spring-jacks busy immediately upon the removal of the substation receiver. Armature 3 also disconnects the winding of cutoff relay 6 from sleeve contacts 152 of the spring-jacks.

The circuit before described as completed through the left-hand winding of relay 10 causes the attraction of the relays armature which completes a circuit'through starting relay ll whose armatures 12 and 13 are attracted, respectively placing ground upon wipers 16 and 17, and through them upon contacts 19 and 20 pertaining respectively to the switches E, E of an idle switch pair. Current then flows from ground through armature 13, contact 1619, through back contact of armature 40, operating relay OR- to battery, and from ground through attracted armature 12, contact 17-20, back contact of armature 31, operating relay OR to battery, causing the energizations of the relays OR and OR. Relay OR- attracts its armatures of which 38 and 39 disconnect trunk conductors La and La from the line wipers 25-27, while armature 37 completes a circult from ground through. pulsating current generator PC, operating magnet OM" to ground, and the said magnet OM advances wipers 232527 to engage the termmal contacts of the first line of the group.

If this line is not that of the calling subscriber, its multiple contacts 22 will be grounded through the back contact of armature 4 of its line relay 2, and as relay OR, by the attraction of its armature 36 has had its winding operatively connected withwiper 23 now engaging a contact 22 of such line, the relay OR is locked and succeeding: pulsations will be transmitted through operating magnet OM, m'oving wipers 23-252'Z over terminals of the non-calling lines until the operating relay- Oll becomes deener gized, which it does as soon as wiper 23 engages the contact 22 of the line of the calling subscriber whose relay 2 is energized and consequently the attracted armature t has removed ground from the multiple contacts 22. \Vit-h the first step of the switch E, off-normal spring ON was shifted to engage its Contact, completing circuit from ground through off-normal relay ONR to battery, armature 31 of this relay freeing operating relay OR from the influence of armature 12 of relay 11, while armature 29 completes a path from ground through 'at t-racted armature back contact of a-rmas ture 32, attracted armature 29, resistance 7, the right winding of relay 10 to battery. The relay 10 being differentially wound and the resistance of 1" coresponding substantially to that of relay 2, the core of relay 10 becomes substantially neutralized, its armature retracted and relay 11 then becomes deene rgized. Off-normal relay ONR by its attracted armature 3O closes circuit from ground therethrough, over contact 2l18, relay 1% .to battery, which relay is operated to close circuit from ground through the pulsating current generator andthe magnet 14:, the said magnet then becoming energized to advance wipers 1G-1718 along the con tacts 1920-21 of successive switch pairs, relay 14 continuing energized and keeping the circuit of magnet 15 closed until wiper 18 engages a contact 21 pertaining to an idle switch pair, in which case, of course, relays ONE and ONR will both be deenergized and the circuit. of relay 1 L will be opened at contacts 30 and ll, the relay de- I energized and further operation of magnet 15prevented... hen switch E has selected a calling line, the retractions of armatures 38 and 39 of relay OR following the denergization thereof, connect link conductors La and La through to the wipers; armature 36 places ground upon the private contacts 22 of the calling line via wiper 23 to prevent another switch E coining to'rest with its wipers engagin contacts of said line which might result if switch E came to rest before switch E came to rest, since as it will be hereinafter more fully explained, relay 2 is only de'e'nergized when both switches of .the pair have completed-their selection.

Referring now-'to switch -E',-the flow of current through the operating relay OK on the attraction of armature 13 at M energizes said relay OR whose attracted ing by way of ground so that an impulse flows through OM and wipers 5 456-58 are advanced a step to engage multiple contacts 53-55-57 of the first link-circuit leading to an A operators position. At-traeted armature 49 has operatively connected the winding of relay OR with private wiper 54, and if this first linlocircuit is busy, contacts 53 will be grounded via wiper 5-4 of another switch E, back contact of armature 49 and release relay RR of said other switch. The windin s of the vrelays RR and OR are so relative y proportioned that an operated relay OR placed in series with a relay RR will receive enough current to retain its armature attracted while the relay RR being inert will not receive sufficient current to cause the attraction of its armaturesi per 54 having engaged the private contact 53 of a busy link-circuit, the operating relay OR will continue locked causing a second impulse'to flow through operating magnet OM and relay OR will continnelocked through successively established circuits similar to that before described, until wiper 54"engages contact 53 of an idle link-circuit such as that shown at A, in which case the private contact 53 will be in its normal condition, namely, on open circuit as shown. The locking circuit of relay OR is therefore interrupted, its armatures 51-52 are retracted and also armature 50, preventing further operation of OM, while armature 49 in its retraction connects ground to wiper 5-4 and private contacts 53 oft-he selected link-circuit, through release relay RR rendering the selected link-circuit busy with respect to other :linlecircuit selecting switches E.

-On the first step of the wipers of the switch E, ofi norinal spring ON was shifted, causing the energization of off-normal relay ONR whose attracted armature 40 freed relay OR from connection with contact 19, while armature 41 placed ground on contact 21. \Ve have thus seen that ground was placed on contact 21 at the two armatures 30 and 41. By this means, con tact 21 pertaining to the switch pair shown in Fig. 1 remains grounded untilboth switches E and E have finally been restored to normal. As these switches may reach normal at different times, it is necessary to have these two independent grounds placed upon contact 21 in order to prevent a possi ble coming to rest of the wiper 18 upon contact 21 of the switch pair before both switches have been fully restored. The at-' traction of armature 42 of off-normal relay ONE completed a circuit fronig'roi'md through attracted armature 48, back-contact of armature 45. attracted armature 42, resistance r, the right winding of-difi'erential relay 10 to battery. This being a branch path of that before traced through said relay winding to ground atarnmture .j

35, and both branch paths being of-negliof relay 10 until both switches E and gible resistance, the provision of these two paths insures continuation of a ncutralizin llow of current through the right winding E! have selected their contacts and come to rest, at which time circuit will be opened through the right winding of relay 10 so far as the particular switch pair is concerned. Simuh taneously with the occurrence of this however, a circuit is completed from ground through cut-oil relay 6 whose attracted armature 9 opens the circuit of relay 2 and the left-hand winding of relay 10 (current being thus practically simultaneously taken from the two differential windings of relay 10 and the operation of its armature prevented), through contact 2627, contact 39, limb La, through contact 52, contact 58-57, through contact 67, relay 62 to battery. Relay 62 is thereby operated (as well as relay 6), and by the attraction of its armature, completes a circuitfrom battery through relay G3, attracted armature of 62, contact 575S to ground through the relay 6. Relay (33 attracts its armature 66'to lock the relay by current flowing to the before mentioned ground, while armature 67 opens the circuit of relay 62 causing its deenergization. Immediately upon the operation of relay 6, relay 5!) was energized to attract armature 31 to close circuit through the call lamp 4 at the A operators position dis playing it, and to attract armature G0 to open a contact in the circuit of release relay RR to prevent its premature operation. The circuit through relay 59 may be traced from ground through said relay over contact contacts 51--38-25--94, attracted armature 7, limb L, hook lever 1 returning over limb L, attracted armature 8, contacts (3G. relay (33 to'battery:

59 is opened at the substation by the subscriber C replacing his receiver, the retraction of armature (30 will cause current to flow from battery through contact Z0, contact 60, attracted-armature 64, contact 5354, normal contact 49,1-el'eas'erelay RR to ground operating relay RR and causing the release of the switch pair E-E as will be hereinafter more fully explained. The A operator observing. the display of the call signal 74. now throws over the levers 72 7 of the listening key associated w1th thecall signal, thus placingl1er..talking fet in""con-' nection with the calling line to learn the Having ascertained this to be the exchange in which the line of D is included,-' she ro s. everv he d st u inga .3K. elongin to the particularcall-signal displayedand her work 'is at an'e'ndL It nvill benoted that whenrelay operated, as hereinbefore described, its armaexchange wanteduby,the:ecallingusubscriber. v

isio ture closed a circuit from ground through the key magnet 68 to battery, the mechanical connection of this magnet to be hereinafter described being such that any distributing key of the link-circuit which may be deressed while the magnet is operated, will held in its depressed position until a subsequent deenergization of the magnet (38 which will allow the depressed key to return to normal. As soon as spring 75 of operated distributing key DK engages its contact, a circuit is completed from grounded armature 65 of relay 63 through contact 75, armature contact 80, winding of relay 84: to battery, the relay 84C thereon attracting its armature 85 to complete a locking circuit for itself through armature S1 to ground, while armature 86 is attracted to remove ground from the multiple private c011- tacts 99 at the banks of the selectors F to rendervthe contacts 99101103 selectable in.character.-. The armature 86 in enga ing its alternate contact completes a circuit rom ground through resistance r", the left winding of relay 87 of the master-switch mechanism M to battery, and the attracted armature of relay 87 completes a circuit for starting relay 88 whose armatures 89 and 90 are attracted, 89 to complete a circuit through contact -95-96, armature 112, operating relay OR to battery, and 90 to complete a circuit from ground through contact 93--9 i, armature contact 123, and operating relay OR to battery. The two operating relays are now energized, closing circuit of their respective operating magnets OM of switch F, and OM of trunk selecting switch F and the two operating magnets advance the wipers of their respective switches to engage the first multiple contacts of their banks. Operating relay OR will remain locked, causing successive cur- .rent impulses to flow from pulsating current enerator PO through operating magnet OM advancing the wipers 10210-:t step-by-step until wiper 100 reaches the contact 99 of distributing key DK whose relay 84 is operated and whose armature 86 has hence been attract-ed to remove the ground from the contacts 99. \Vhen this occurs, the operating relay 0R which, during the operation of the switch up to this time, remained locked by current flowing over successive paths extending through attracted armature 105, and contacts 99 to ground at armatures 86 of all unoperated keys, be-

comes deenergized, opening circuit through operating magnet OM, armature 105 then placing ground on the multiple contacts 99 of the selected key, while armatures 10710S which were held attracted by relay OR during the operation of the switch, fall bacli'to j a ain connect wipers 102-40 with limbsijt-azb'.

With the first step of switch F, ofi-normal spring ON was shifted to complete circuit through oil-nonnal relay ONR- whereby contact- 96 was, by the operation of arn'ialure 112, disconnected from operating relay 0 while armature 114 completed a circuit for relay 91 of the masterswitch upon whose operation magnet 92 initiated travel of wipers 93 95-97, past contacts 91-9698 of busy trunk switch pairs F F. Armature 113 of the off-normal relay ONR completed a circuit from ground through contact 111, resistance r and the right winding of relay 87 to battery, and as resistance 7' is substantially equal to resistance 1- in circuit with the left-hand winding of relay 87, the relay becomes substantially neutralized, the relays armature is retracted causing the denergization of starting relay 88, thus preventing other switch pairs from before starting as wipers 939597 move in search of idle contacts.

The circuit before described as completed through operating relay OR of switch F, operates the relay, whose, armature 117 is attracted to close circuit through operating magnet OM and pulsating current machine PC magnet 0M then stepping wipers 12" 129131 a step to enga e the contacts forming multiple terminals 0 the first trunk circuit TT terminating in a B operators cord at the distant exchange. If this trunk circuit-is busy, its contacts 126 will be grounded throu h the normal contact of armature 116 oi the operating relay OR of another trunk selecting switch F via the wiper 127 of said trunk selecting switch and the multiple 126 of the trunk line engaged by the wiper 127 of the other switch, and a locking circuitwill therefore be completed via its attracted armature 116 for relay OR of the seeking switch F .of .I ig; 1, armature 117 continuing attracted and a second impulse will flow through magnet 0M advancing the wipers a second step to engage the multiple contacts of the next trunk circuit TT. If this trunk is also busy, another locking-circuit for relay OR? will be completed via wiper 127,"and successive-impulses will flow through magnet '01P advancing the wipers step-'hy-step until the contacts of an idle trunk line are reached, at which time, owingto the normal insulated condition of itsmultiple contacts 126 as shown. in Fig. 1, relay OR is deenergized, opening-circuit through magnet OM by the" retraction ofarmature "117,

while'armature 116 places ground upon the' multiples of the contact 126 engaged by,..

wiper 127, holding them busy and armatures 118 and .119 complete the circuit over the With the first step of the wipersfof the .limbs TT, of the selected trunk-throu h contacts' 128- 129 and 130'"131 to lim s -;Lb-Lbof the switch pain shifted to close its contact operating 01tnormal relay ()NR whose armature 123 disconnected terminal 9-1 frond relay 0R armature 125, placed a busy ground upon contact 98 of the switch pair and armature 124 completed a branch to ground for neutralizing resistance 1 i i order that the windings of relay 87 may cont-im 1 e to neutralize one another untilsu'cl 'time as both siyitches F -F' of the pair have completed their: selections, at ti'hicli' tinie current is taken practically simultaneous froin' the contact '77, tolb attery' Said relay:

a: a eta es. a it a t rl l w i c'uifi Q'f eii ia a a r'fifi h'd e g i Q indicates that the subscriberls line has lpeen 'extendedtlii t'iilgh were B oper'ator at the egtchafii gei: The eration of relay 78 1, 1: rsultm g frd'rri thejest'ab ishing of the circuit 'cau'sing lthe attraction i sifiif a e, t z ir er 9' h circuit of relay $4: wh'eis theru Orr retracted arniature 86 interrupts'the' ow of current through resista'rice r and the left winding of relay 87,

whileiarmature $0 of relay 79 opns a contact in' the original energizing circuit of relay 84, preventing it from being again operated; Arn iature 83 o't' relay '('9 short circuit s'fthe inding of relay 78 to' caus e its cleenerg'ization.

It: will reri embred that the floir of,

current operating relay 781' also trayels over thewinding of relay 115' whose attracted armaturescau's'e the en ergiz'ations of the release relays RR and RR of switches FF, respectiyely. The attracted armatures 111 and 122 of these relays open the circuits through the right windin'gofrelay S7 at a time practically simultaneous with the open ing ot the circuitthrough the left winding of the said relay 87, as before described, thus preventing the attraction of the armature of said relay. Attracted armature 82 of relay 79 completes a locking circuit for relay 79 extending from battery through said attracted armature 82, contact 99100, re-' tr'acte'd armature 105 to' ground.

The attracted armature of relay 137 asso ciatedrtith the cord at the B operators posi; tion completes a circuit causing the energlzation of relay 136, whose attracted armature closes a normally open contact. in the circuit of call signal lamp 134, while relay 132 now energized by current from battery over trunk limb T, thence following the talking circuit. as indicated by the heavy conductor to the left, through closed contact 76 at the A opcrators position and to ground through armature 61, by the attraction of its annature closes another normally open contact in the circuit of lamp 13 so that thfla'iiip is non? displayed, currentfiowing therethrough froin battery through said larnp .and to ground at the retracted left armature of relay 139. It will be obser'yed that if the calling subscriber at this time has his receiver rela'ced, this act has opened thecircuit of re ay 59 at the A o erator s, position and caused its deer ergiziatioii, retraction of arni'atu're G0 resiiltiii in the restoration of the switch pair n hile' the r'aaaiaa of armature 61 o'pfen'sthe circuit of relay, 132' and the rt-ra'ctio'n'ot the a'rfr'ia'tui of relay 132 then caste-ale restoration or are. switch pair F'F. ,j the; det'a'illjo f xiiliich' 6 er'zitioffs if ill be hereafter ,fullyflescrib ed'.

The operator in response t'o the' of signal 134:, will throw, ot er lefiers'72 and 73, andas certain from calling. sub scriber the number of the line ti afited, the talking circuit being traced to ,tlieleft .(i'vr the heavily iiiarked conductors aridtlirohgh suhstatioh C,' current for coiiyersationai purposes being supplied to the calling'line from attery at' the K opera'tors iboard' through the impedances'of relays and 63, v The B' operator ha'vin learned the number wanted, that of the called subscriber assumed to be D, inserts the plug of the cord associated with the displayed signal 134' intoa' n'mltiple jack of the called line-easing contacts 150 453 and 1'51.152. Assuliiing 'that this line is an idle line, the sleeve contact 152 will be of the same potentiallas ground, be ing connected thereto through the Winding of cut-'ofi relay 6, and current will flow froin the intermediate or eight volt-tap of battery through the windings of polarized test relay 1,419, retracted armature of relay 139, contact- 146, contact 151152, IIOIIl'lfll contact oi iii-mature?) of the line circuit of the called line D, cutofi' relay (ito ground, energizing relay (5 whose attracted armat'ures'S and 7 connect li1nbs' IrL to jack contacts 153-.-152, While arlnatii'res 7 and 9 I open the ci'rc iiit s of lin'e relayfi 'lhe direc tionof this current flowis suchas to tilt the ounded armature oftest relay'149 to the eft, completing circuit. from the said grounded armature, throiigh the winding of sleeve supervisory relay 139 Whose attracted i right armature locks the said relay-over a circuit extending therethrough over contact .1416, cantata. 1 514152 6 pimd, through cutoft relay .6, and opens the circuit attest relay 149 whosea'rnia'tiire returns to normal. 13)

' the :other stations The left armature of relay 139 opens the circuit of the call signal 134, causing its restoration, and by engaging its alternate contact, effects the display of the calling supervisory signal 155. The actuating means for springs K'Z: and K- 0 etc., of the four arty line ringing keys are normally locked E mechanism controlled by the armature of magnet 154, the energization of this magnet being required to unlock them to render the selected key capable of being actuated by the operator, as will more. fully appear from the hereinafter contained descriptions of the mechanical drawings.

. The ringing generators G-G -G G are each provided with its appropriate ringing keyfsprings Kk, 11 etc one such key, foreach generator being provided in association'with each B operators cord circuit.j.=The said generators are so arranged as to deliver ringing current of varying frequencies to the end of enabling the B operatorto s'electivel'y signal the desired one oft-he stations on .aparty line such as that of subscriber D, themulti le taps only to D- D Dibeing shown.

Sucha systemis' described and shown in patent to William W. =Dean #779,533, issuedanuary 10, 1905, for party line telehone. stem.

Theattraction of the left-hand armature of relay 139 in addition to displaying lamp 155, establishes a branch pathfrom ground through said left armature of relay 139, armature 17 6 of relay 141, contact 144, key magnet 154 to battery, causin the actuation of magnet 154, WlllCll, by its mechanical connections, now unlocks the four ringing keys of the cord circuit. The operator new actuates the ringin key appropriate to throw over springs and the mechanical connections of magnet 154 are effective to holdthe actuated key in the ringing position, springs K7c thus being placed in engagement with and held in engagement with their associated contacts, it being as-.

sumed that generator G associated with lever K delivers current of the roper frequency to ring the tuned bell 0F substation D. Rin g current then flows from generator G t rough contact K, normal contact of armature of relay 140, contact 147, con-' tact 150-153, attracted armature 7 of cut-- off relay 6, through hook lever 1 and the bell at substation D, causing it to ring, returning over attracted armature 8 of relay 6, contact 3, contact152-15l, contact 146, at traeted'right armature ofrelay 139, through said relay, and to ground through the central battery.v Constantly operating interrupter I alternately connects and. disconnects shifted spring is from ground, encrgizing and de'einergizing the relay 140 whose alternately attracted and retracted armaturc whenattracted, disconnects generator G from tip contact 150 of the plug, thereupon operatively connecting relay 138 with said tip contact, and when retracted, connects generator G with contact 150 periodically ringing the called substation bell in the well known manner.

As soon as thecalled subscriber D in response to the signal, has removed his receiver and relay 140 has its armature attracted, a circuit will be completed from ground through the relay 13S, attracted armature of relay 140, contact 147, contact- 150153, the current then flowing over the before traced path for ringing current over the line of subscriber D except that it now passes through the hook lever and its alternate contact returning over limb L and the before traced path, through relay 139 to battery. This causes the energization of tip supervisory relay 138 whose attracted armature opens the circuit of supervisory lamp 155, and by engaging its alternate contact, energizes relay 141. Armature 176 of relay 141 causes the deenergization of magnet 154, and said armature 170 by engaging its alternate contact, locks the relay 141 by current traversing the attracted left armature of relay 139 to ground. The armature 17 5 of said relay 141 closes a normally open contact in the tip strand of the cord, while a corresponding normally open contact in the sleeve strand has previously been closed on the operationof relay 138. The mechanical connections of relay 141 are such that when the actuated ringing key on the deenergization of magnet 154 leaves its ringing position, its full return to normal is prevented, and the key held in an intermediate or so called indicating position in order that the B operator may know which key she has actuated'should it become necessary to ring the called subscriber a second time. The

subscribers C and D are now 111 conversation, the talking circuit being traced from substation O to substation D over the heavily marked conductor, talking current being supplied to the line C through relays 59 and (33 and to the line of D through relays 138 and 139.

If the line of D be in use at the time the B operator inserts the plug of her cord circuit in the multiple jack of said line.,the sleeve contact 152 will be connected to 'the twenty-four volt tap ofthe exchange battery,-if the subscriber isa calling subscriber and his line has not yet been selected-by 'a line selector as will be understood from the preceding description of the selection of line C. If he be a calling subscriber and his line has ,been selected, sleeve 1 contact 152 tors position, through winding ofrelay-63,

and owing to the relativeresistances of relay, 1' (33, cut-oii relay (3 of the calling line and the v other instrumental'ities' in the circuit,-.-, there .125 will be connected to battery at the A opera- 3' will be a potential at the sleeve contact 152 of the p -l of from thirteen to fifteen volts. If the li-ne'c'alletl for be bus as a called line, the sleeve contacts 152 of-its jacks will be connected with the twenty four Volt ta-p of the exchange battery throu h a; relay-189, and'this relay 139 and. cat uit relay 6 and the other instrumentah ities in the circuit are so proportioned thatthc sleeve contacts-152 of the line sprin jacks will be at a potential of a proximately thirteen to' fi'fteerr vo1ts-.- In any of these cases-it will be observed that theotential at the sleeve contacts of the spring jacks of the busy line is greater than the potential at the intermediate tap at the exchange bat tery indicated as eight volt-s and upon the insertion-of a connectin -plug, into a mat tiple' jack of-abusy line, current will flow through tlie='pblari2edtestrelay l4c9"in-a direction op osite to that in which it flowed when its-associated 'lug was connected with the multiple; jack 0 the idle line; Orr con-- motion m de with-- the busy li'n'e, therefore the' rounded armature-of polarized: testrelay 149 will be tilted in the opposite di rection', that is, to the rlght,- comp'letin' a cir'ci'ii't t-hroughthe "right windin of re ay- 142 Whose attracted armature 1455 will close a lockin circuit for the relayy'extendingthrough the contact 145-146; pla mntact 151, to sl'ee've' 152 of aijaekof th'e'liusy line to ground througl'i its cutoff relay 6.- Said armature 145 immediately thereafter causesspring 146 to" disengage its normal contact,

opening the circuitof test relay 149.- A1"' matu'r'e 14? disconnects the ringing 'c'onductor from the tip 150 chime-plug,- armature 148 operatively connects the busy signal and of relay 59 whose retracted armature 61 will open the circuit of relay 132 to display supervisory signal 135, both supervisory signals being then displayed. The operator" thus has an indication "enabling her, if her cords are all in use, to take down the con nection without waiting for the calling sub scriber to transmit the disconnectsignal;

It will be observed that whether conneetion is made with an idle or busy line, as

soon as the B operator has inserted the-plug of one of her cords into the'spring-jaclcof 'a wanted line, the sleeve supervisory relay 139 isenergized either over a circuit extendin to ground through cut-oil relay 6 if the called line is idle, or by a circuitextending to ground through armature 143 of relay 142 if the called line is a busy line. The left-hand'armature of this relay 139 in addition to the functions previously mentioned, has that of opening a normally closed contact in the circuit of relay 133-, which is the relay'employed for restoring to normal the two switch'pairs used in the connection as well as the'distributing key at the A operators position. As soon therefore, as the B operator inserts the plug into the jack of the wanted line; the previously existing control of the calling subscriber over the releasing circuits is destroyed, and the release is then controlled by the B operator.

Let it be assumed that-the called line is found idle, that conversation is finished and the two subscribers C and D have replaced theirrecei'vers. When subscriber D does so, the movement of heel: level- 1 opens the circuit thro'u'glisupervisory relay 138 and its right armature again'closes the circuit of callingsupervisory signal 155. \Vhen subscriber C replaces his receiver, the movementof hook lev'er 1 opens the circuit of relay 5 9, and itsarmatures G061 are'retr'aeted, ar- 'mat-ure G1- opening the -circuit extending ;throi'igh "contact 76 of distributingkey DK, jover'condugtor's M, Lb, trunk-conductor T relay- 132 to battery; the arinatures of relay 132- then' return to normal, the right-hand armature closing 'a circuit from ground at .the attracted left armature of relay 139, thro'ugh'the retracted right armature of relay 132, answering supervisory signal 135 to battery 'causing the display of said"sig-' -nal. The two supervisory signals 135 and 155 being now displayed, the B operator withdraws the plug of the cord from the jack of the" called line. This deiinergizes relay 139 and its retracted right armature again connects test relay 1&9 operativcly to the sleeve 151 of the plug, while its retracted left armature opens the circuit of supervisory signal 1'55, and said armature by engaging its back contact, completes a circuit from ground through said armature, at-

tracted armature of r'elay 136. retracted armature of relay 132, relay 133 to battery.

The attracted armature of relay 133 opens the T circuit previously extending from ground through relay 137 over conductors T',' LIL-and relay l'lfi conductor M and relay 69 to battery, causing the deenerg zation o frelays 115 and 69. Thedetnerglzw tion of relay 115 results-in the -res'torationf of the switch-pair FQF, while the dot nergization of relay 69 results in the restora- 'tion of-thedistributing key DlCand ,of the i switch pairF EC- Tracing first in detail the result bf tlie d eenergization of relay 115, it will be remembered that the armatures of said relay closed the circuits of release relays RR and RR which relays remained operated from the time relay 115 was first energized, their armatures 110 and 121 respectivel havin locked their relays through 0 -normzil s rings ON and 0N respectively. Hence t iese relays will remain energized .uutil the respective switches are restored;to.zero and off-normal springs ON. and ON then restored. The restoration of the left .armature of relay 115 completes a circuit from ground at oft-normal spring ON through said retracted armature, attracted armature 109 of release relay RR, operatingrelay OR to battery. 10perating relay OR therefore becomes energized and will continue energized, its' armature 106 causing successive actuations ;of operating magnet OM to move the wipers otswitch F contin'uously inthe same direction as that in which they were originally moving until they have completed onerevolution and theswitch being restored .to normal, off-normal spring ON is shifted,=opening the=eircuit of oft-normal relay ONR release relay RR and operating relay ORA. Similarly, the

retraction of the right armature of relay 115 closes a circuit from ground atofi-normal spring ON through-retracted: right armature of relay 115, attracted armature 120 of release relay RR, through operating relay OR to battery, and the attracted armature 117 of the-operatin --relay, OR causes suc-' cessive actuations 0 operating magnet OM until the wipers of the switch F reach normal when the shifting of spring 0N to nor mal deenergizes relays ONR R11 and 0R As soon as in the restoration of switch F,

wiper 100 disengages contact 99 of the distributing key DK, circuit was opene through relay 79 and its armatures retracted.

The deenergization of relay 69 before de-.

scribed caused the retraction of its armatures of which armature-70 completed a oir cuit as follows: from ground through the winding of release relay RR at switch E,

normal contact of armature 49, contact.

54-53, attracted armature 64, retracted armature 60, retracted armature 70 and to.

battery, operating release relay RR whose.

armature 46 closes circuit from ground at.

oil-normal spring ON. through attracted armature 46, attracted armature 40, o'perat' ing relay ORCto battery. Armature 44 of relay RR on its attraction was efiective'to lock" the relay RR by a circuit extending from ground through'the relay winding, attracted armature 44, attracted armature 43 and to. battery, and as ofi-normal'relay ONR re mains operated until oil-normal sprin' ON. is shifted back, the three relays ONR RR; and OR remain energized. Operatin re-' lay OR by its attracted armature 50c oses a circuit for current impulses through operating magnet OM and the said magnet advances the wipers of switch E step-by-step until the switch completes a revolution, and on its return to zero, cit-normal spring ON opens circuit through relays ONE and 011. The denergization of the former Opening the circuit of the release relay RR. On the operation of the release relay RR, its armature 47 completed a circuit from ground through said attracted armature through release relay RR of switch E to battery. Attraeted armature 33 of relay RR, locked the said relay over a circuit extending to ground through attracted armature 28 of oft-normal relay ONR, while armature 34 completed a circuit from grounded olinormal spring ON through said attracted armature 34, through attracted armature 31, operating relay OR to battery. The relays OLR, RR and OR- now remain locked, while operating magnet OM steps the wipers of switch E around to zero when the shifting of oft-normal spring ON results in the defnergization of the three relays ONR, RR and OR.

As soon as,operating relay OR of switch E was energized, the attracted armature 52 opened the circuit of relay (33, the retraction of whose armature 65 opened the circuit of key -magnet 68 allowing the restoration of the distributing key DK. The attraction of armature 52 also causes the deenergizatiou of cut-ofi relay 6 of the calling line, placing the line circuit of the calling line in its normal condition.

Referring again to the cord circuit at the B operators posit-ion, it will be observed thatv the deenergiz'ation of relay 139 was effective to open the circuit of relay 141 allowing the actuated ringing key to return from its indicating position to its normal position. The release operation, when the B operator has inserted the plug of her cord into the spring-jack of a busy called line, follows upon the withdrawal of the plug and the consequent deenergization of relay 139-in the same manner as that previously described. It the calling subscriber replaces his receiver before the B operator has insertedthe connecting plug into the springjack, the act musesdenergization of relay 59 and consequentially the deenergization of relay 132, and since relay l39 is at this time denergized and its leftha-ncl armature has remained retracted, the release operations proceed as'before described. It the calling subscriber replaces his receiver before connection has been established be; tween the distribut ing key ot-the A o'pera'- tors' positionandthe B operators cord cir;

cuit,'his.a'ct dene'rgizes re ay 59 causing the retraction of armature 60 and this is effective to cause the releaseof the switch-pair E-E as before described, because owing 115, M, relay 78.

to the fact that relay 69 had not, been operatcd, such operation only occurring when connection is established through to a B operators position, the armature 7 O of relay 69 has remained retracted, permitting the release circuit for switch E to be established. If the callin subscriber restores the switch pair E-E during the time the switch F is seeking the contacts of operated distributing key DK, the deenergization of key mag net- 68 occurring-before selection is made, restores the distributing key DK.

lhe ground having been previously taken ofi contacts 99 by the operation of armaturc' R6 of relay 84, which relay locked itself by a circuit extending through armature S1 of relay 79 to ground, the trunk selecting switch F will now proceed to select contacts 9910l-103 of the distributing key as if the same had remained operated. .'When this selection has occurred and switch F has also completcd'itsselection, a circuit is closed from ground at.- the cord circuit through relay 137 ove-r'T, Lb, back contact of armature 83 to battery throlwh impedance 156.. The resulting currentflow operates relay 115 causing the energization of relays RR and RR and also operates relay 78 whose attracted armature energizes for a moment, relay 79. The attraction of armature 83 of the latter relay 7 9 opens the battery connect-ion extending through impedance 156 which permitted the energizing of relays 115. and 78 as described, and the deenergizations of these relays follow; that of 115 causing the restoration of switches F-F in the manner before described. It is thus seen that under all circumstances until the'operator inserts the plug of the selected trunk into a jack of :1 called line, the calling subscriber by replacing his recciver, accomplishes circuit changes resulting in the complete restoration of whatever switches have been operated.

The relays 136 and 133 are preferably rendered slow to release their armatures after-current has once been closed through their windings in order that when relay 133attracts its armature to start the release oper ation, as before described, which also results in the falling back of the armature of relay 136-a relatively long time may elapse before relay 136 allows the retraction of its attracted armature, and of course relay 133 remains energized long time to the end that a sutlicient time may elapse before relay 133 releases its armature for the release operations at switch pair F-F to proceed far enough to cause the -energization of operating relay ()R of.

switch F so that on the retraction of the armature of relay 133, contact 119 may be open, and the ground through relay 137 again placed on limb T of the trunk line rotary shaft- 179 to which is thereafter a relatively Carr) n :pawls 159 j 1160 held against-the ratchet by their associated spring may have no effect upon relay 115. To render their armaturcs slow to retract, copper shells may as indicated. be placed about the cores of relays 133 and 136.

Referring now to Fig. 2, showing the master-switch mechanism which may be considered as that shown-at M in Fig. l, corresponding reference characters have been supplied to Fig. 2. The operatin magnet 15 is provided with an armature riven pawl 17S arranged to engage the teeth of the ratchet 15.7 fastened to a suitable supported fastened the angularly disposed contact-wipers 157 of which there are'threc sets fastened to shaft 179, one-above the other. One of the angular wipers of each of the upper and middle sets being shown as broken, discloses one arm of each of the middle and lower wiper sets. Ten sets of, contacts, 19-20.-21 are shown in Fig. 2' corresponding to the similarly designated terminals in F ig. 1, the wipers l617-1 8 shown in said Fig. 1 being represented by the common strips 16 '1718 'in Fig. 2, strip 16 extending around .underneath contacts 19, strip 17, underneath contacts 20 and strip 18 underneath contacts 21, wipers 157 having in themselves no circuit connections but being arranged to cross the successive contacts of the three levels with their common strips successively int-he operation of the switch. The structure shown in F ig. 2 is also adapted for use in connection with the circuits shown at- M in Fig. 1.

F igs .:3, 4, 5, 6 and 7 illustrate a mechanical structure that may be employed in connection with the circuits of switches E E and F-F- in Fig. 1. As these switches preferably have a continuous movement in one direction in their operation and a further movement in the same direction in their restoration to normal, I preferably arrange the switching contacts in a circle and place beneath each set a common strip extending around the circle, the switch wipersin themselves having no circuit connection, hutserw ing when the switch is operated to cross successive contacts of the three sets provided, to their respective common strips. In the said Figs. 3 to 7, referencecharacters corresponding to those of switch E in Fig. 1 are supplied for convenience of reference. A suitably supported rotary shaft 182 is provided to which is fastened the circular ratchet 180together with the wipers 161 and 23, 25 and 27, shown in Figs. 5 and 7.

The operating magnet OM is provided with the armature 15S extending the length, of. the magnet and engaged by the stiff spring 163 for restoringflit after being attracted by the magnet on the dcnergizat-ion thereof.

'ed by the armature 158 are'the two 

